The United Kingdom approves the development of atomic weapons.
The US Atomic Energy Commission issues a memo on "Medical Experiments on Humans." The memo reads, in part, "It is desired that no document be released, which refers to experiments with humans and might have adverse effect on public opinion or result in legal suits. Documents covering such work should be classified secret."
U.S. Secretary of State George Marshall announces European Recovery Program, sometimes referred to as the Marshall Plan.
William Penney begins the design of a plutonium bomb for the United Kingdom.
George F. Kennan, U.S. Chargé d’affaires in Moscow, outlines the policy of political containment of the Soviet Union in his article "Sources of Soviet Conduct."
The United Kingdom's first atomic reactor at Harwell comes into operation.
British physicist Klaus Fuchs meets with Soviet secret police agent, Alexander Feklisov, in London and describes certain structural characteristics of the hydrogen bomb.
Nuclear war plans of the U.S. Joint Chiefs of Staff consider 150 "Nagasaki type" sufficient to defeat the USSR. The nuclear weapons stockpile is still small (20-50), but growing.